Association for Academic Surgery
Vitamin D Status of Morbidly Obese Bariatric Surgery Patients1

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Background

Abnormal vitamin D levels are common in bariatric surgery patients. The incidence of deficiencies and the response to therapy is not accurately delineated. The purpose of this study was to define the vitamin D status of patients who undergo either a malabsorptive (gastric bypass) or restrictive (adjustable gastric band) bariatric surgery both prior to and after surgery.

Methods

A retrospective analysis was performed on patients to undergo bariatric surgery from July 2002 to February 2007. Serum levels of vitamin D (Vit D), parathyroid hormone (PTH), and calcium were analyzed.

Results

Mean patient age was 45 y; 82% of patients were women. Of 127 total patients, 84% were Vit D deficient preoperatively. These patients had a higher preoperative body mass index (BMI) than those with normal Vit D levels on initial assessment (BMI 44 versus 50 kg/m2, P < 0.01). A correlation was found between preoperative BMI and Vit D (r2 = 0.12, P < 0.01) and PTH levels (r2 = 0.07, P < 0.01). One year following gastric bypass surgery, 20% of patients with elevated PTH levels had normal Vit D levels. The incidence of observed deficiencies for adjustable gastric band versus gastric bypass did not differ statistically at any interval.

Conclusions

Morbidly obese patients seeking bariatric surgery are often deficient in Vit D, a fact that should be accounted for when evaluating the impact of bariatric surgery on Vit D levels. Elevated BMI and increasing degrees of obesity may be risk factors for both Vit D deficiency and secondary hyperparathyroidism. Despite normal Vit D levels, some gastric bypass patients continue to show elevated levels of PTH.

Introduction

The use of bariatric surgical procedures in the United States rose 6-fold from 1990 to 2000 and has continued to rise substantially in the current decade 1, 2. Bariatric surgical patients are at risk for developing a variety of nutritional deficiencies postoperatively. Certain bariatric procedures may lead to alterations in Vit D metabolism and calcium absorption 3, 4. These changes may lead to derangements in bone homeostasis, putting patients at risk of developing osteopenia and osteoporosis. Prevention of these abnormalities includes both supplementation and routine monitoring [5].

The preoperative and postoperative Vit D status of patients undergoing bariatric surgery has not been well-defined. Additionally, the response to directed therapy in patients with altered gastrointestinal anatomy has not been accurately delineated. The purpose of this study was to define the preoperative and postoperative Vit D status of patients undergoing either laparoscopic Roux-en-Y gastric bypass (RYGB) or laparoscopic adjustable gastric banding (LAGB).

Section snippets

Materials and Methods

A retrospective review was conducted of data prospectively collected on patients to undergo either RYGB or LAGB surgery in the UW Health Bariatric Surgery Program between July 2002 and February 2007. This review was approved by the Institutional Review Board. Our surgical technique for RYGB has been previously described in detail [6]. Briefly, a less than 30-mL isolated gastric pouch is created. The standard length of the biliopancreatic limb is 50 cm. A 100 or 150 cm Roux limb is fashioned,

Results

There were 360 patients to undergo RYGB and 63 patients who had LAGB surgery in the study interval. Of these patients, 127 (30%) had preoperative Vit D levels (79 RYGB and 48 LAGB). For those with preoperative Vit D levels, mean age was 45 y and 82% of the study patients were women. Of the 127 patients with preoperative Vit D levels, 84% were Vit D deficient on initial baseline assessment (Table 1, Table 2). Patients who were Vit D deficient preoperatively had a significantly higher

Discussion

We have demonstrated that in our Midwest bariatric surgery program, the incidence of Vit D deficiency prior to surgery is significant (84% overall; 88% RYGB, and 75% LAGB). Other studies have reported preoperative Vit D deficiencies among bariatric surgery patients ranging from 54% to 90% 7, 8, 9, 10. This variability may partly be attributed to the differences in definition of deficiency used by the institution. For example, the aforementioned authors used deficiency thresholds ranging from 20

Acknowledgments

This research was supported by the Herman and Gwendolyn Shapiro Foundation and the University of Wisconsin Department of Surgery.

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      Fig. 2 represents studies that have a number of participants of at least 50 per study group or subgroup, based on bariatric surgery type. It shows that mean 25(OH)D levels were ≤ 20 ng/ml in fifteen studies [51–65], and between 20 and 30 ng/ml in the others [66–77]. The weighted mean 25(OH)D levels (ng/ml) did not differ significantly between studies, classified according to the baseline participants' mean BMI (mean BMI ≥ 50 kg/m2, mean BMI between 45 and 50 kg/m2 and mean BMI ≤ 45 kg/m2) (Fig. 2).

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      We also included 1 paper reporting work underway by our group during the period in which this literature review was performed, bringing our total citations to 31. Preoperative vitamin D status was reported in 29 studies (Supplementary Table 1), which altogether contain a mixture of observational and experimental data from 3776 patients [25–27,31–33,36–38,53,58–76]. According to these studies, the prevalence of preoperative VDD (<20 ng/mL) ranges from 13% [59] to>90% [37], the majority of which reported prevalence>50% [27,33,36,37,58,60–65,67–69,72–74,76].

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    Presented as an Oral ‘Quick Shot’ at the February 2008 Academic Surgical Congress, Huntington Beach, CA.

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